1 // Copyright (c) 2018 Google LLC 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef SOURCE_OPT_FOLDING_RULES_H_ 16 #define SOURCE_OPT_FOLDING_RULES_H_ 17 18 #include <cstdint> 19 #include <unordered_map> 20 #include <vector> 21 22 #include "source/opt/constants.h" 23 24 namespace spvtools { 25 namespace opt { 26 27 // Folding Rules: 28 // 29 // The folding mechanism is built around the concept of a |FoldingRule|. A 30 // folding rule is a function that implements a method of simplifying an 31 // instruction. 32 // 33 // The inputs to a folding rule are: 34 // |inst| - the instruction to be simplified. 35 // |constants| - if an in-operands is an id of a constant, then the 36 // corresponding value in |constants| contains that 37 // constant value. Otherwise, the corresponding entry in 38 // |constants| is |nullptr|. 39 // 40 // A folding rule returns true if |inst| can be simplified using this rule. If 41 // the instruction can be simplified, then |inst| is changed to the simplified 42 // instruction. Otherwise, |inst| remains the same. 43 // 44 // See folding_rules.cpp for examples on how to write a folding rule. It is 45 // important to note that if |inst| can be folded to the result of an 46 // instruction that feed it, then |inst| should be changed to an OpCopyObject 47 // that copies that id. 48 // 49 // Be sure to add new folding rules to the table of folding rules in the 50 // constructor for FoldingRules. The new rule should be added to the list for 51 // every opcode that it applies to. Note that earlier rules in the list are 52 // given priority. That is, if an earlier rule is able to fold an instruction, 53 // the later rules will not be attempted. 54 55 using FoldingRule = std::function<bool( 56 IRContext* context, Instruction* inst, 57 const std::vector<const analysis::Constant*>& constants)>; 58 59 class FoldingRules { 60 public: 61 FoldingRules(); 62 63 const std::vector<FoldingRule>& GetRulesForOpcode(SpvOp opcode) const { 64 auto it = rules_.find(opcode); 65 if (it != rules_.end()) { 66 return it->second; 67 } 68 return empty_vector_; 69 } 70 71 private: 72 std::unordered_map<uint32_t, std::vector<FoldingRule>> rules_; 73 std::vector<FoldingRule> empty_vector_; 74 }; 75 76 } // namespace opt 77 } // namespace spvtools 78 79 #endif // SOURCE_OPT_FOLDING_RULES_H_ 80
